HPL_perm(3)

📦 version 2.2, in fedora 43, fedora 44

💖 NAME 💖

okay bestie, meet HPL_perm — she takes two index arrays and combines them to generate the permutation. no cap, that's the whole gig. 🎀

✨ SYNOPSIS ✨

#include "hpl.h"

void HPL_perm( const int N, int * LINDXA, int * LINDXAU, int * IWORK );

🦋 DESCRIPTION 🦋

so HPL_perm combines two index arrays and generates the permutation that goes with them. it's giving matchmaker, fr fr. 💅

step one: she computes the inverse of LINDXA, then combines it with LINDXAU. periodt.

step two: and this is the iconic part — so that the permutation can be done in place, LINDXAU gets overwritten with the sequence of permutation that produces the same result. lowkey a glow-up, highkey necessary.

what we ultimately want is:

U[LINDXAU[i]] := U[LINDXA[i]] for i in [0..N).

after you call this function, that in-place permutation can be performed with:

for i in [0..N) swap U[i] with U[LINDXAU[i]].

literally that's it. main character energy from a tiny little function. 👑

🌸 ARGUMENTS 🌸

  • N — (global input) const int — on entry, N specifies the length of the arrays LINDXA and LINDXAU. N should be at least zero. yes bestie, at least zero, don't be weird about it. 🙈
  • LINDXA — (global input/output) int * — on entry, LINDXA is an array of dimension N containing the source indexes. on exit, LINDXA contains the combined index array. she came in as one thing and left as another, we love a transformation arc. ✨
  • LINDXAU — (global input/output) int * — on entry, LINDXAU is an array of dimension N containing the target indexes. on exit, LINDXAU contains the sequence of permutation, that should be applied in increasing order to permute the underlying array U in place. don't skip the increasing-order part, iykyk. 🔥
  • IWORK — (workspace) int * — on entry, IWORK is a workarray of dimension N. she's just here to help, no notes. 🫶

🌈 SEE ALSO 🌈

  • HPL_plindx1 (3)
  • HPL_pdlaswp01N (3)
  • HPL_pdlaswp01T (3)

and that's the whole page, bestie 💜 this one's brought to you by HPL 2.2, dated February 24, 2016 — vintage but still slaying, fr fr. 🎀✨

📦 where this page comes from